Although the induction of tumors in human beings by exposure to environmental chemical carcinogens is well documented and although we have shown that normal cells in culture are readily mutated by such carcinogens, no system has been developed to reproducibly transform human cells in culture with chemical carcinogens. The advantages of being able to carry out such transformation of human cells are (1) it would provide the closest analog we have to studying human chemical carcinogenesis in vivo; (2) it would allow us to test directly the hypothesis that a causal relationship exists between somatic cell mutation and cell transformation, and, finally, (3) it could serve as the basis for an important system for identifying potential chemical carcinogens. Therefore, we propose to work out the methods required to establish such an in vitro chemical carcinogenesis system for detecting transformation in human cells (Fibroblasts and epithelial) in culture, taking into consideration the conditions that have been demonstrated to be necessary for the successful transformation of animal cell cultures. Using populations of human cell types selected because they possess characteristics similar to those of one or more of these successful animal cell systems, we will: (1) expose the cells to direct-acting "ultimate" carcinogens, using repeated doses if necessary, (2) permit subsequent cell division in order to allow for "fixation and expression of transformation," (3) identify "candidate transformants" by certain morphological and/or functional characteristics, and (4) correlate these with the ability of the "candidate transformants" to produce tumors in athymic nude mice. We will also examine the effect of promotors on the ability of human cells to be transformed.